Bovine somatotropin (bST), usually in the form of recombinant bST (rbST), is a broad-acting polypeptide hormone which influences a wide range of complex functions in cattle, including growth rate, maturation, milk production and the like.
Studies on the use of bST in finishing beef cattle to provide commercially advantageous methods of preparing beef cattle for slaughter have successfully increased the average daily gain and slaughter weight of the cattle. However, bST treatment typically decreases the dressing percentage of the cattle.
When cattle are slaughtered, the body weight consists of carcass weight, non-carcass body components, and digestive fill. The carcass weight is the weight of the carcass, including the kidneys, but not including the head, hide, hooves, viscera including digestive fill, and other internal organs. The ratio of the carcass weight of the animal to the total body weight in percent is referred to as the dressing percentage.
bST administration to beef cattle during the finishing stage of growth has also been found, when continued substantially until slaughter, to increase the proportion of weight gain which appears in non-carcass components. This calculation can frequently be made from data presented in the prior art references. Thus, bST-induced increase in body weight has typically been disproportionately allocated to commercially less-valuable non-carcass components of the animals.
When cattle are being prepared for slaughter, it would be advantageous to increase significantly both the dressing percentage and the carcass weight, since in this way the investment in feed supplementation and treatment during the finishing stage would reduce cost per unit of meat. Heretofore, there has been no reliable method of significantly increasing the dressing percentage of cattle receiving bST and preferentially allocating the increase in body weight to the more valuable carcass components.
Fabry et al., "Influence de l'hormone de croissance sur la production de viande chez les genisses," Reprod. Nutr. Develop. Vol. 27 (2B) 591-600 (1987) showed that the dressing percent value in heifers of the Belgian White Blue breed injected daily with about 50 milligram/day (mg/d) of bST dropped from 58.9% to 57.9%. Only about 36% of the weight increase in the bST-treated heifers appeared in the carcass components.
Early et al., "Growth and Metabolism in Somatotropin-treated Steers: I. Growth, Serum Chemistry and Carcass Weights," J. Anim. Sci. 68:4134-4143 (1990) showed that the dressing percent value in Hereford steers daily injected with about 20 mg/d of bST dropped from 53.8% to 51.8%. Early et al., "Growth and Metabolism in Somatotropin-treated Steers: II. Carcass and Noncarcass Components and Chemical Composition," J. Anim. Sci. 68:4144-4152 (1990) showed that most of the body weight gain in such steers was in the non-carcass components. Only about 12% of the weight increase in the bST-treated steers appeared in the carcass components.
Mosely et al., "Recombinant Bovine Somatotropin Improves Growth Performance in Finishing Beef Steers," J. Anim. Sci. 70:412-425 (1992) showed in two experiments that increasing dosage of bST administered by daily injection to cross-bred steers in the finishing stage of growth, while increasing feed efficiency ("FE") and average daily gain ("ADG"), decreased dressing percentage. In a first experiment, dosages of rbST of 33 and 100 ug/kg decreased dressing percentage from 62.7 to 61.3% and a dosage of 300 ug/kg decreased dressing percentage from 62.7 to 58.7%. In a second experiment, treatment with rbST at 8.25, 16.5, or 33 ug/kg decreased dressing percentage from 63.2 to 62.5 or 62.6% while treatment with 66 ug/kg rbST reduced dressing percentage from 63.2 to 61.9%. The cattle were slaughtered at constant weight. These studies suggested that as average daily bST dose increased, the extent to which dressing percent was diminished also increased.
Wagner et al., "Effect of growth hormone (GH) and estradiol (E.sub.2 .beta.) alone and in combination on beef steer growth performance, carcass and plasma components," showed that subcutaneous injections of a biweekly-administered oil formulation containing 960 mg bST to cross-bred beef steers decreased dressing percent from 63.0% to 61.1%. In combination with estradiol, rbST treatment decreased dressing percentage from 64 to 61.4%. The biweekly bST treatment, in the presence or absence of estradiol, resulted in all of the weight increase being allocated to the non-carcass components.
In Enright et al., Effects of long term administration of pituitary-derived bovine growth and estradiol on Friesian steers, J. Anim. Sci. 68: 2345-2356 (1990), daily injections of bST were discontinued at 22 weeks whereas estradiol treatment was continued until slaughter at 30 weeks. Carcass analysis was not obtained at the end of bST administration, but was conducted eight weeks after the last bST injection. Sandles et al., Anim. Prod. 44:21-27 (1987) had shown that bST effects were lost about 5 weeks after cessation of bST injection. Thus, carcass data obtained eight weeks post bST injection may not be valid for examining bST dressing percentage responses. bST administration to the finishing stage cattle ending eight weeks prior to slaughter generally had no significant effect on carcass weight and had no significant effect on dressing percentage.
Preston et al., "Comparative effects of BST and steroidal growth promotants in feedlot steers," American Society of Animal Science, American Dairy Science Association, Midwest Section, Mar. 23-25, 1992, reported that when bST was administered by intraperitoneal sustained release pellets (first-order release) dressing percent was not significantly changed. See, also, Preston et al., "Role of protein level and source on the response of feedlot steers to levels of somatotropin," Journal of Animal Science, Volume 71, Supplement 1, Abstract 173.
Rumsey et al., Growth Response to an estrogenic growth promoter and recombinant bovine somatotropin (bST) in young beef steers, FASEB 1994 pA158, Abstract Number 917 reported results of treating young cross-bred steers with bST, estrogen, and a combination of bST and estrogen. Rumsey et al. did not report dressing percentage, but provided data from which the dressing percentage for the various treatments could be estimated. These data indicated that treatment with estradiol increased dressing percent (56%), that bST treatment decreased dressing percent (53%) and that concurrent treatment with bST and estrogen/progesterone resulted in no change in dressing percent (54%), all relative to controls (54%).
In McBride and Mosely, Influence of Exogenous Somatotropin on the Components of Growth in Ruminants, the authors summarize the work on bST in cattle and sheep: Body weight gain is often accompanied by an increase in non-carcass components and the carcass weight may not be significantly increased.
Thus, summarizing these articles, while estrogen alone had been observed to increase dressing percentage in cattle not being treated with bST, there remains a need for an effective treatment which includes administration of bST and which will significantly increase both dressing percentage and carcass weight of cattle in the finishing stage of growth.
These and other advantages can be achieved by those skilled in the art in accordance with the invention herein disclosed. The invention is not limited to the embodiments specifically disclosed herein, but by the claims attached hereto interpreted in accordance with law.